1. Field of the Invention
The present invention relates to batch, batchwise-continuous, and continuous processes for recovering aluminum chloride from deactivated alkylation catalyst complexes by low-corrosion hydrogenation using an aluminum catalyst. Most specifically, the present invention relates to the hydrogenation of a complex sludge of aluminum chloride and olefinic hydrocarbon compounds using an aluminum powder catalyst in the presence of hydrogen gas; the aluminum powder also acting as a reagent to remove hydrochloric acid from the reaction mixture to reduce the corrosiveness and cost of the hydrogenation step.
2. Description of the Prior Art
The use of aluminum chloride based homogeneous complexes to catalyze hydrocarbon conversion reactions such as alkylation and isomerization is known in the art. Alkylation processes for the production of gasoline that use a soluble alkylaluminum chloride--based catalyst, such as the catalyst and process disclosed in U.S. patent application Ser. No. 08/370,056 by Sherman, now U.S. Pat. No. 5,593,569, have been shown to be more cost effective and environmentally friendly than conventional sulfuric acid and hydrofluoric acid alkylation processes. As the alkylation reaction in such processes approaches completion, the homogeneous catalyst degrades to a less active state and forms a separate sludge phase. The present invention is directed to the recovery of aluminum chloride from this sludge for recycle to produce the soluble catalyst.
Aluminum chloride can be recovered by hydrogenation of the sludge at high temperature (200.degree. C.) and high pressure (3000 psig), but the combination of aluminum chloride and hydrochloric acid produced during hydrogenation is very corrosive at high temperatures for a carbon-steel reactor, making the hydrogenation step expensive. The corrosion rate can be reduced by reducing the temperature and pressure or by reducing the amount of hydrochloric acid present. While rhodium or palladium, both well-known hydrogenation catalysts, can be used to lower temperature and pressure, these catalysts are expensive. It has now been found that metallic aluminum (a less expensive agent) is an effective hydrogenation catalyst in the presence of hydrogen gas for these homogeneous, high bound-hydrocarbon content, alkylaluminum chloride--based catalysts and promotes the liberation of aluminum chloride and paraffinic by-products at a lower temperature (150.degree. C.) and pressure (1500 psig) than non-catalytic hydrogenation. The metallic aluminum also scavenges excess hydrochloric acid utilized in allylation or produced in the hydrogenation process, thereby greatly reducing reactor corrosion.
The prior art contains numerous methods for recovering spent catalysts from alkylation processes but none using aluminum to catalyze the hydrogenation of alkyaluminum chloride--based catalysts. For example, U.S. Pat. No. 2,517,692 teaches the regeneration of deactivated aluminum halide catalysts from sludge utilizing hydrochloric acid in conjunction with an olefin and aluminum as a reagent. Hydrogenation is not practiced and the aluminum is sacrificial, reacting with hydrochloric acid to produce more aluminum chloride. The process is non-catalytic and is a net producer of aluminum chloride relative to the present invention. Similarly, U.S. Pat. No. 3,846,334 deals with regeneration of sludge to produce a "reactivated complex," not aluminum chloride, using aluminum with hydrochloric acid and benzene, not hydrogen. The present invention regenerates aluminum chloride using hydrogenation and no aromatic hydrocarbon reagents. Also, U.S. Pat. No. 3,476,825 teaches the use of aluminum powder and hydrochloric acid to produce aluminum chloride in-situ, not to regenerate catalyst from a sludge. In a separate step, hydrogen was used to regenerate the catalyst but not in the presence of aluminum.
Further examples include U.S. Pat. No. 4,017,584 which uses aluminum that has been pretreated with hydrogen chloride to disproportionate the aluminum chloride from the sludge complex at temperatures not exceeding 100.degree. C. Unlike the present invention which practices catalytic hydrogenation, no hydrogen is used. Also the aluminum is stoichiometrically consumed in the reaction. For every three moles of aluminum chloride released from the sludge, one mole of aluminum is converted to aluminum chloride. In the present invention, aluminum is catalytic in the hydrogenation step and is only consumed by reaction with any net excess hydrochloric acid in the system resulting from the presence of more than stoichiometric amounts of alkylation catalyst complex activator which is also liberated during hydrogenation. The method taught by the '584 patent did not produce aluminum chloride when applied to the high-hydrocarbon (about 46 weight % hydrocarbon) alkyaluminum chloride--based catalysts that are the focus of the present invention. U.S. Pat. No. 1,582,131 discloses non-catalytic hydrogenation of aluminum chloride catalyst residues with the recovery of aluminum chloride by distillation. U.S. Pat. No. 2,211,207 describes hydrogenation in the presence of heavy metal halides, it does not teach the utility of aluminum as a catalyst for aluminum chloride recovery.
None of the aforementioned patents teaches the use of aluminum powder as the hydrogenation catalyst for aluminum chloride recovery which is the subject of this application.